docs: def _switch_tz_offset_sql(self, field_name, tzname):
          """
          Returns the SQL that will convert field_name to UTC from tzname.
          """
          field_name = self.quote_name(field_name)
          if settings.USE_TZ:
              if pytz is None:
                  from django.core.exceptions import ImproperlyConfigured
                  raise ImproperlyConfigured("This query requires pytz, "
                                             "but it isn't installed.")
              tz = pytz.timezone(tzname)
              td = tz.utcoffset(datetime.datetime(2000, 1, 1))
  
              def total_seconds(td):
                  if hasattr(td, 'total_seconds'):
                      return td.total_seconds()
                  else:
                      return td.days * 24 * 60 * 60 + td.seconds
  
              total_minutes = total_seconds(td) // 60
              hours, minutes = divmod(total_minutes, 60)
              tzoffset = "%+03d:%02d" % (hours, minutes)
              field_name = "CAST(SWITCHOFFSET(TODATETIMEOFFSET(%s, '+00:00'), '%s') AS DATETIME2)" % (field_name, tzoffset)
          return field_name